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  19 <a name="boost.log.attributes.timer"></a><div class="titlepage"></div>
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  21 <h2><span class="refentrytitle">Class timer</span></h2>
  22 <p>boost::log::attributes::timer &#8212; A class of an attribute that makes an attribute value of the time interval since construction. </p>
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  24 <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
  25 <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../../attributes.html#header.boost.log.attributes.timer_hpp" title="Header &lt;boost/log/attributes/timer.hpp&gt;">boost/log/attributes/timer.hpp</a>&gt;
  26
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  28 <span class="keyword">class</span> <a class="link" href="timer.html" title="Class timer">timer</a> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">attribute</span> <span class="special">{</span>
  29 <span class="keyword">public</span><span class="special">:</span>
  30   <span class="comment">// types</span>
  31   <span class="keyword">typedef</span> <span class="identifier">utc_time_traits</span><span class="special">::</span><span class="identifier">time_type</span><span class="special">::</span><span class="identifier">time_duration_type</span> <a name="boost.log.attributes.timer.value_type"></a><span class="identifier">value_type</span><span class="special">;</span>  <span class="comment">// Attribute value type. </span>
  32
  33   <span class="comment">// <a class="link" href="timer.html#boost.log.attributes.timerconstruct-copy-destruct">construct/copy/destruct</a></span>
  34   <a class="link" href="timer.html#idm45711348449920-bb"><span class="identifier">timer</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span>
  35   <span class="keyword">explicit</span> <a class="link" href="timer.html#idm45711348449200-bb"><span class="identifier">timer</span></a><span class="special">(</span><a class="link" href="cast_source.html" title="Class cast_source">cast_source</a> <span class="keyword">const</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  36 <span class="special">}</span><span class="special">;</span></pre></div>
  37 <div class="refsect1">
  38 <a name="idm45554750299680"></a><h2>Description</h2>
  39 <p>The timer attribute calculates the time passed since its construction and returns it on value acquisition. The attribute value type is <code class="computeroutput">boost::posix_time::time_duration</code>.</p>
  40 <p>On Windows platform there are two implementations of the attribute. The default one is more precise but a bit slower. This version uses <code class="computeroutput">QueryPerformanceFrequence</code>/<code class="computeroutput">QueryPerformanceCounter</code> API to calculate elapsed time.</p>
  41 <p>There are known problems with these functions when used with some CPUs, notably AMD Athlon with Cool'n'Quiet technology enabled. See the following links for more information and possible resolutions:</p>
  42 <p><a href="http://support.microsoft.com/?scid=kb;en-us;895980" target="_top">http://support.microsoft.com/?scid=kb;en-us;895980</a> <a href="http://support.microsoft.com/?id=896256" target="_top">http://support.microsoft.com/?id=896256</a></p>
  43 <p>In case if none of these solutions apply, you are free to define <code class="computeroutput">BOOST_LOG_NO_QUERY_PERFORMANCE_COUNTER</code> macro to fall back to another implementation based on Boost.DateTime. </p>
  44 <div class="refsect2">
  45 <a name="idm45554750293296"></a><h3>
  46 <a name="boost.log.attributes.timerconstruct-copy-destruct"></a><code class="computeroutput">timer</code>
  47         public
  48        construct/copy/destruct</h3>
  49 <div class="orderedlist"><ol class="orderedlist" type="1">
  50 <li class="listitem">
  51 <pre class="literallayout"><a name="idm45711348449920-bb"></a><span class="identifier">timer</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre>
  52 <p>Constructor. Starts time counting. </p>
  53 </li>
  54 <li class="listitem">
  55 <pre class="literallayout"><span class="keyword">explicit</span> <a name="idm45711348449200-bb"></a><span class="identifier">timer</span><span class="special">(</span><a class="link" href="cast_source.html" title="Class cast_source">cast_source</a> <span class="keyword">const</span> <span class="special">&amp;</span> source<span class="special">)</span><span class="special">;</span></pre>
  56 <p>Constructor for casting support </p>
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  64 <td align="right"><div class="copyright-footer">Copyright &#169; 2007-2016 Andrey Semashev<p>
  65         Distributed under the Boost Software License, Version 1.0. (See accompanying
  66         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>).
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